Steel Wire Rope Failure...

[pscandrett]

The great thing about aperture synthesis using interferometry...

You understand I am trying to find a simple analogy I can grasp.

 

Your organ thing... I'm not sure how close that is as resonance isn't quite the same as interference. Interferometers are normally used to measure small distances or disturbances (see wikipedia) The Michelson-Morley experiment tried to use this to study the speed of and nature of light.

 

The best analogy without talking about frequencies I can think of off the top of my head is when you look through lots of lenses in a kaleidoscope - each lens gives you an bit of the image, but taken together you can see a bit more of it if you put all the images together. It's a really bad analogy but it sort of works. The interferometry is the method of taking each lens's image and sticking them all together.

 

(Don't forget that a radio telescope doesn't give an 'image' in itself - it's basically just looking at a pixel on the sky, and gives a value of brightness, so you need to scan the sky anyway to get any sort of detail or structure.)

 

This ESO page goes into it a little more, and uses the example of water waves interfering. This phys.org article explains it a bit too, pointing out that it's all to do with the path being slightly different between two telescopes, so it takes the signal slightly longer to reach one than another - and by combining it together carefully you can deduce more about the source.

 

I fear the mods if I write more as we're not talking about anything to do with stage stuff, even tenuously, now!

[Junior8]

Thanks - that makes sense.

[ImagineerTom]

Let me bring this back on to topic - for the last 4 years the big dish at jodrel bank has been being upgraded so hasn’t actually done any science stuff - it’s only use has been as a prop and backdrop for the festivals and gigs so technically it’s a prop (operated by an automation technician) now. QED we can talk about huge radio telescopes on here :-p

[richardash1981]

To paraphrase Tom's point about why big dishes are not considered as important:

• A single big dish has a massive amount of gain, but not great directionality. So you can pick up very quiet things (like the cosmic microwave background, echoes of the big bang, discovered at Arecibo), but not if there is anything louder nearby.
• An array of smaller dishes, with the outside ones a long way apart (now global, e.g. UK and Australia) has far less gain, but tremendous directionality - as directional as if you built a dish the size of the earth (in theory). So you can get really high resolution images.

As for interferometry, it's closely related to how a shotgun mic works - all the little slots in the microphone act like dishes, feeding into the one long tube which combines the sound in such a way that you get a really directional microphone. For radio astronomy, it's all about dedicated fixed-delay fibre optic networks to link the dishes, and the correlator (pscandrett) is like the microphone capsule - where all the signals get combined. Which is why (now high-gain, low-noise microphones are available) no-one uses parabolic reflectors for audio recording!

 

Another example of interferometry is phased array loudspeakers (columns, line arrays etc.) where each source is not very directional, but the system as a whole is. So you see it's very relevant to audio!

 

[IRW]

I fear the mods if I write more as we're not talking about anything to do with stage stuff, even tenuously, now!

 

To be fair, there's very little else of great interest going on around here at the moment, for obvious reasons...With all the wonderful insights from those of you who actually understand what you're talking about, I think this must surely qualify for 'most interesting thread of 2020', even if I say so myself!

[marktownend]

That's a much better clip of the actual failure than on the BBC article I'd seen, and at the start of the 2nd clip (around 55 seconds in) you can see that the cables were already in the process of failing, the white paint was missing where some strands had already pinged, so presumably the drone had purposely been put up to look at the failure as it progressed.

 

I like how if you look at the aerial view of Arecibo and zoom out, it looks like it's in the middle of nowhere in otherwise virgin forest, but then you realise that it's only a few km from the coast and civilisation and you can see the creep where roads and homes have gradually snaked into the forest.

[pscandrett]

Someone's done a ten minute analysis in slow-mo explaining what failed and in what order, which gives some insight into what happened in those few seconds.

 

[Jivemaster]

 

Is a vid detailing the increasing mass of the cable supported components.

[Junior8]

That Scott Manley video is an example of what youtube users can do well and what the mainstream media would have made a complete pig's ear of.

[sunray]

That Scott Manley video is an example of what youtube users can do well and what the mainstream media would have made a complete pig's ear of.

Yes I agree.

 

With a little bit of polishing it would make a good TV program.

Edited December 7, 2020 by sunray

[GridGirl]

Slightly off topic but still important and on the subject of radio telescopes: I do hope everyone here has seen the film The Dish. It’s centred around the Parkes radio telescope which played a big part in broadcasting pictures from the Apollo 11 moonwalk. Wonderful Australian film - well worth a watch if you haven’t seen it.

[themadhippy]

well worth a watch if you haven’t seen it.

Especially the american national anthem scene

[richardash1981]

Is a vid detailing the increasing mass of the cable supported components.

 

He makes a point I hadn't appreciated in here - Arecibo was one of very few Radar Astronomy sites - with a 1MW radio transmit power, plus that huge disk, it could bounce radio waves off Saturn! This also meant it was by some margin the best tool we had for locating incoming asteroids which might hit earth - because if you want to know what the orbit of a body is, 2D observations aren't going to cut it, and Radar is your best bet. All gets explained here (from three years ago):

With hindsight, you can see the maintenance backlog in the condition of many of the parts ...

 

[pscandrett]

Yeah, sorry, I mentioned that in passing really; it was a great radar system too.

 

You link to Tom Scott's video - the accompanying mostly head-cam footage ('behind the scenes') is worth a watch, too, now that it's gone...

[bigclive]

That Scott Manley video is an example of what youtube users can do well and what the mainstream media would have made a complete pig's ear of.

Yes I agree.

 

With a little bit of polishing it would make a good TV program.

 

No need. Scott Manley is doing just fine on YouTube.

He'd probably find it extremely frustrating working with the old fashioned television industry.

It would reduce the quality and quantity of his content.

 

Modern media is much more honest, relaxed and engaging. And you can actually chat with the presenters online.